The present invention relates to a power transmission system for a general industrial device and an aircraft. More specifically, the present invention relates to a torque limiter in which a coupling portion for transmitting a rotational force shuts off or separates when a load exceeds a predetermined value.
A movable wing surface forming a part of a flight control system of an aircraft is called a rudder surface (flying wing surface or moving wing), and includes an aileron provided on a main wing as a main rudder surface, and an elevator and a rudder provided on a tail wing. The movable wing surface also includes a slat, a posterior-border slap, a flight spoiler, a gland spoiler and so on provided on the main wing as an accessory rudder surface. The main wing is composed of a wing and respective rudder surfaces (slat, slow speed aileron, high speed aileron, flight spoiler, gland spoiler and posterior-border slap). An aircraft body is controlled through an operation of the rudder surfaces and the tail swing.
FIG. 3 shows a high-lift system of an aircraft. The high-lift system is a system in which a rudder surface of a flap/slat provided in a main wing is operated in order to obtain lift of the aircraft when the aircraft takes off and lands. It is necessary to operate each rudder surface of the right and left wings simultaneously (left rudder surfaces 33a and 34a, and right rudder surfaces 33b and 34b). A drive motor 30 is disposed in the middle portion of the aircraft for rotating right and left torque shafts 32 simultaneously through a gear box 31. In view of safety, it is necessary to operate the right and left rudder surfaces symmetrically (left rudder surfaces 33a and 34a, and right rudder surfaces 33b and 34b).
FIG. 4(a) is a view showing a high-lift system equipped with torque limiters (left wing torque limiter 35a and right wing torque limiter 35b). The high-lift system has power for operating the right and left rudder surfaces with one drive motor 30. The torque limiter limits torque transmitted to the left and right sides only as necessary and prevents excess torque from being transmitted. With the torque limiters, it is possible to reduce a size and weight of a component at a downstream side of the torque limiter as the torque limiter limits the maximum output torque.
The torque limiter of the high-lift system needs to shut off torque greater than a required torque for driving one wing, and needs to rotate the right and left shafts symmetrically within a predetermined level. The torque limiter mainly includes one type in which a shaft is fixed to a case and the other type in which a shaft becomes free for shutting off torque. In the high-lift system, since it is necessary to operate the right and left wings symmetrically, the type in which a shaft is fixed to a case is used. In the torque limiter in which a shaft is fixed to a case, it is necessary to stop the shaft instantly. Accordingly, when the torque limiter is operated, a large surge torque is generated due to inertial energy of the drive motor 30, so that a measure for controlling the surge is separately required.
FIG. 4(b) is a view showing a high-lift system equipped with a surge torque buffering apparatus 36. In the high-lift system, a torque limiter in which a shaft is fixed to a casing is provided on an output shaft of each of left and right wings (left wing torque limiter 35a, right wing torque limiter 35b). The surge torque buffering apparatus 36 is provided for reducing the surge torque generated by inertial energy. The surge torque buffering apparatus 36 is formed of a spring and the like.
FIG. 5 is a cross sectional view of a torque limiter in which an output shaft 2 is to be fixed. An input plate 3 connected to a drive shaft 1 is fitted in a bearing provided in a housing 9. At an opposite side, the output shaft 2 is supported on a bearing provided in the input plate 3 and a bearing provided in a housing 10. The input plate 3 is connected to the drive shaft 1 to rotate, and the output plate 4 is capable of rotating and moving on the output shaft 2 in an axial direction. An output plate 4 is fitted into the output shaft 2 to be movable back and forth. A ball ramp portion 5 is disposed between the input plate 3 and the output plate 4, and has lamp channels wherein a ball 6 is retained. A preload spring 7 is provided for pressing the ball ramp portion 5 in an axial direction so that the ball ramp portions 5 is not activated up to a certain torque. A brake portion 8 increases a torque according to a load in an axial direction generated when the ball ramp portion 5 is activated.
FIG. 6 shows a structure of the ball ramp portion 5. An upper portion in FIG. 6 is a side of the input plate 3, and a lower portion in FIG. 6 is a side of the output plate 4. Lamp channels with smooth slopes are provided on both sides for sandwiching the ball 6. The preload spring 7 presses the output plate 4. A depth and a size of the lamp channel and a size of the ball 6 are determined such that the ball ramp portion 5 is not activated up to a certain torque.
When the input plate 3 rotates, the lamp channel at a side of the input plate 3 moves in the right direction in FIG. 6. As a result, a driving force (torque) acts in an arrow direction through the ball 6, and a pressing force acts in an arrow direction on the output plate 4. When a torque greater than a predetermined value is applied, the input plate 3 moves further in the right direction in FIG. 6. As a result, the ball 6 rolls against resistance of the output plate 4 pressed by the preload spring 7 with a certain force, and increases a distance between the both plates. Accordingly, the brake portion 8 stops the output plate 4, thereby shutting off the torque to the output shaft 2. As described above, when a rotating torque greater than a predetermined value is applied to the drive shaft 1, the coupling portion for transmitting the rotational drive limits the torque transmission.
Another type of torque limiter is able to shut off a torque when an overload is applied and maintain a position of the shut off (for example, refer to Japanese Patent Publication (Kokai) No. 07-293576).
In the conventional torque limiter with the structure described above, when the transmitting torque exceeds a predetermined value, the torque limiter instantly stops the rotational shaft, thereby generating a torque surge due to inertia of the rotational body. In order to reduce the torque surge, it is necessary to provide the surge torque buffering apparatus 36 such as a slip clutch as shown in FIG. 4(b), thereby increasing cost and weight, and lowering reliability.
In the view of the problems described above, the present invention has been made, and an object of the present invention is to provide a torque limiter with low cost, light weight and high reliability, wherein a downstream portion of a system is not affected when the transmitting torque exceeds a predetermined value due to the torque surge and so on.
Further objects and advantages of the invention will be apparent from the following description of the invention.